1. Field of the Invention
The present invention relates to a reciprocating piston engine having a cylinder block, at least one cylinder head, and at least one replaceable cylinder liner, whereby a piston is slideably disposed in each cylinder liner, and a combustion chamber delimited by the cylinder head, the cylinder liner, and the piston is provided. The cylinder liner is supported by means of a liner shoulder on the cylinder block, and the cylinder head end face of the liner shoulder is provided in the region contiguous to the combustion chamber with a raised edge and in the remaining (outer) area with a recess that is radially open to the outside and is bounded by a circumferential raised portion which is directed towards the cylinder head. Disposed between the latter and the cylinder block is a plate-like cylinder head gasket, of solid metal, that projects into, or is disposed in, said recess.
2. Description of the Prior Art
It is known in reciprocating engines having replaceable wet cylinder liners to use flat or plate-like cylinder head gaskets to prevent leakage of combustion gases between the cylinder liners and the associated cylinder head. Generally, these gaskets consist of a metal-reinforced soft material and are rimmed in the region of the combustion chambers with metallic edges of U-shaped cross section. When the cylinder head is screwed onto the cylinder block, the rim bead of the gasket around the combustion chamber is pressed onto the clamping shoulder of the cylinder liner, with a certain minimum pressure being necessary to ensure satisfactory sealing of the combustion chamber. The necessary concentration of the pressure in the region of the gasket bead relative to the remaining surface of the gasket, which provides sealing of the water and oil passages between the cylinder block and the cylinder head, is generally achieved in that the surface of the cylinder liner on which the gasket bead is seated is provided with a closely toleranced projection above the cylinder block sealing surface.
Drawbacks of this configuration are as follows:
(a) Especially where the liner shoulder bears near the top of the cylinder block, it is necessary to adopt extremely accurate and difficult-to-manufacture tolerances for the depth of the counterbore in the cylinder block and the depth of the liner flange or shoulder.
(b) The thicknesses of the cylinder head gasket, frequently being made up of several layers, in the region of the gasket rim and the remaining surface of the gasket, call for very close matching of the tolerances.
(c) The initial loading of the cylinder head bolts has to be applied within close tolerances.
(d) The inevitable remaining tolerances on dimensions and bolt forces cause a very wide scatter of the compressive forces, especially in the region of the gasket rim bead. The resulting high bearing pressures are liable to cause deformation of the bore of the cylinder liner whereby, at the same time, the abutment in the cylinder block for the liner flange can be overstressed and can fail while, on the other hand, the bearing pressure on the remaining area of the gasket will decrease, which may cause water and oil leakages. Conversely, gas leakage is liable to occur due to an accumulation of tolerances of low bolt forces, and little projection of the flange seated on the cylinder block or a flange that is even lower than the top of the cylinder block.
Therefore, the arrangement described, in particular in the case of modern high-performance engines of light-weight construction with an inevitably low surplus of initial cylinder head bolt loading and simultaneously high combustion chamber pressures, represents only a compromise with substantial disadvantages.
Some improvement of the combustion chamber sealing can be achieved if, instead of the composite cylinder head gasket described initially, a solid sheet of the same thickness is used and is forced into a groove that extends all the way around in the cylinder head in the region where the liner is sealed by a raised portion which extends all the way around on the projecting flange of the cylinder liner, which bears on the cylinder block. As a result, the gas seal is improved, in addition to the pressure acting on the liner sealing flange. At the same time, it is possible--in principle this is also possible in the arrangement described initially--to provide sealing of the water and oil passages between the cylinder block and the cylinder head even more selectively by inserting elastomeric elements. This arrangement enables sealing of the combustion chamber to be effected with lower initial loads for the cylinder head bolts, while avoiding leakages at the water and oil passages, due to the elasticity of the sealing elements.
A drawback of the last-described system is that, just as in the case of the arrangement initially described, the tolerance conditions are liable to result in undesirably high pressures on the sealing face of the cylinder liners, resulting in the aforementioned negative consequences, namely deformation of the cylinder liner bore and overstressing of the cylinder block. Furthermore, the groove in the underside of the cylinder head calls for costly machining on a lathe. Also, accurate and expensive centering of the cylinder head relative to the cylinder liner is necessary to ensure that the raised face on the liner and the groove in the cylinder head coincide. Partial contact of the cylinder head in the remaining area of the gasket is obtained only after the cylinder head has been deformed by tightening of the bolts so that, as a result, there are no clearly defined conditions regarding the cylinder head contact in the remaining area of the gasket.
It is therefore an object of the present invention to avoid the above-described drawbacks in a reciprocating engine of the type initially referred to, without the need for expensive measures to narrow down the tolerances; in other words, a reliable gastight seal for the combustion chamber is to be ensured at all times while permitting large manufacturing tolerances, i.e. tolerances on the dimensional design of cooperating parts and for the cylinder head tightening torques.